Cap Ill Iary Tube

8/9/2019 Cap Ill Iary Tube

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CAPILLARY TUBE

This case study demonstrates the modeling of a capillary tube.

Capillary tubes are used as expansion devices on some vapor-

compression refrigeration systems. The refrigerant used in this case

study is R22..

GENERAL INDUSTRY



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P a g e 1

CHALLENGE :

The objective of the simulation is to determine the mass flow through the capillarytube.

BENEFITS:

This case study demonstrates the modeling of a capillary tube. Capillary tubes are

used as expansion devices on some vapor-compression refrigeration systems. The

refrigerant used in this case study is R22..

SOLUTION:

Flownex was used to determine the mass flow of R22 through a capillary tube given

the inlet pressure and temperature and the outlet pressure. This case studydemonstrated Flownex’s ability to calculate two-phase flow in a tube including

choking at the exit.

GENERAL INDUSTRY

The objective of the simulation is to determine the mass flow through the

capillary tube.

Flownex was used to determine the mass flow of R22 through a capillary

tube given the inlet pressure and temperature and the outlet pressure. This

case study demonstrated Flownex’s ability to calculate two-phase flow in a

tube including choking at the exit.




P a g e 2

INTRODUCTION

This case study demonstrates the modeling of a capillary tube.

Capillary tubes are used as expansion devices on some vapor-

compression refrigeration systems. The refrigerant used in this case

study is R22.

SYSTEM DESCRIPTION

A tube with a length of 400 mm and an inside diameter of 2 mm is

considered. The fluid is R22 with an inlet pressure of 1990 kPa and

an inlet temperature of 43 ºC. The outlet pressure is 680 kPa.

OBJECTIVE OF SIMULATION

The objective of the simulation is to determine the mass flow

through the capillary tube.

FLOWNEX MODEL

The Flownex model of the tube is shown in Figure 1.

Figure : Flownex model of capillary tube.

Element 2 is a Restrictor with Discharge coefficient (Flownex’s RD

element). This type of element is used to model the exit losses,

which can be very large. RD elements can model exit losses

accurately, even in the case of choked two-phase flow.

CAPILLARY TUBE

This case study

demonstrates the

modeling of a capillary

tube. Capillary tubes

are used as expansion

devices on some

vapor-compression

refrigeration systems.

The refrigerant used in

this case study is R22.




P a g e 3

DESCRIPTION OF SIMULATION

A pressure and temperature boundary condition is specified at

node 1 while only a pressure boundary condition is specified at

node 2.

RESULTS

Flownex calculates the mass flow as 0.0467428 kg/s.

Figure 2 shows the variation of pressure and Figure 3 shows the

variation of quality over the length of the tube. The large drop in

pressure at the exit indicates that the flow is choked at the exit.

CONCLUSION

Flownex was used to determine the mass flow of R22 through a

capillary tube given the inlet pressure and temperature and the

outlet pressure. This case study demonstrated Flownex’s ability to

calculate two-phase flow in a tube including choking at the exit.

Figure : Variation of pressure over the length of the tube.

0

500

1000

1500

2000

2500

0 100 200 300 400

P r e s s u r e [ k P a ]

Distance [mm]

Flownex was used to

determine the massflow of R22 through a

capillary tube given the

inlet pressure and

temperature and the

outlet pressure. This

case study

demonstrated

Flownex’s ability tocalculate two-phase

flow in a tube including

choking at the exit




P a g e 4

Figure 3: Variation of quality over the length of the tube.

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0 100 200 300 400

Q u a l i t y [ ]

Distance [mm]

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Cap Ill Iary Tube